HR pistons in VQ35DE block.. no go without mods..
 

I'm starting a new thread, and hoping that a mod will sticky this.. so you guys can avoid the same problem that I've encountered.

Stock HR pistons, with VQ35DE rods/crank will not work, without either slightly fly cutting the edges of the pistons, or, by using a slightly thicker Cometic head gasket.

Without mods, and with clearances set a little on the loose side (any performance built engine), the pistons just barely make contact with the quench pads in the cylinder heads.. So, I would recommend fly cutting the edges on each piston, up to about 1/8" from the valve reliefs. I would cut it around .010" deep, to avoid any/all potential contact.

Here's a pic to show what I'm talking about..

http://www.fi-r.net/images2/VQSwapFi...tonContact.jpg

The area in the rectangle, shows how contact with the quench has cleaned the piston of carbon. We're not talking much here, but, there's enough contact to cause noise. By cutting the area shown with a mill, you can increase clearance by about .010", just to be safe, and get away with putting HR pistons into your DE block. You should be able to get this done at any competent machine shop for around 100.00 for 6 pistons. Or, you could spend a few more bucks, and get Cometic gaskets that are a little thicker, and avoid having to cut the pistons alltogether.

Anyway.. just wanted to share some useful info..

Travis

Ok, so I did some research.. and found that the HR pistons have the same dome volume as Rev-up pistons. The difference in compression ratio between the two, comes from changes in the combustion chamber volume. So, we know that HR pistons have a 5cc's of dome volume. We can get pretty close in guestimating that the .010" of material removed will equate to roughly .5cc.. MAYBE 1cc.. max.. So here we go..

Bore- 3.759"
Stroke- 3.204"
HG thickness (compressed)- .028"
Deck height- -.007" (after removing material/splitting the difference with the rest of the remaining (taller) material where we didn't take .010" out)
Piston dome volume- -4.5cc (with material removed)
Combustion chamber volume- 56cc's

This give us a static compresion ratio of 11.53:1. I would say that it will be plus/minus 1 tenth, depending on the exact dome volume, but, it's safe to say that it'll be within .5cc's of my estimate. So, betwen 11.4:1 and 11.6:1 static compression with this HR pistons, fly cut .010", in a DE block with DE heads/rods/crank.

Travis

Seems like you're still having alot of fun with those vq swaps in the specs, travis. Are the HR pistons forged?

They are still hypereutectic cast.

Stuck.

Thanks Nismology..

I snapped a few pics of a piston that has been cut down .010" to clear the head..

http://www.fi-r.net/images2/VQSwapFi...onContact1.jpg
http://www.fi-r.net/images2/VQSwapFi...onContact2.jpg

The piston's edges are now flush with the bore. :)

Travis

Thread closed. Will consider reopening if the OP has something new to add or if someone has a legitimate question that has not been addressed.

I think there's some incorrect information in the thread. OP said the HG thickness was 0.028" compressed. I think he's referring to the cometic gasket which is 0.030" uncompressed. The stock HG is 6mm (0.023") uncompressed for both the DE and HR from what I can gather.

I ordered some 0.040" cometic gaskets, but they're taking eons to arrive. I think that I might cancel that and go with the 0.030" ones that are more easily available. Could I go with the 0.030" gaskets without having the pistons fly cut??

I used stock gaskets.. I got the .028" compressed thickness figure from Clark Steppler @ JWT. I assume that it is correct.. But, with stock gaskets, you definitely will have interference issues. So, I would go with a .040" gasket from Cometic.

Travis

The HR is thicker I believe. I've got both..

I finally got around to putting in HR pistons with the .040" Cometic head gaskets. It works perfectly with no interference issues whatsoever. I had to do it that way because no machine shop around me would fly cut the pistons.

It gave my a small, but nice bump in power throughout the powerband and I have no more visible blue smoke on hard acceleration, even with only 250 miles on the rebuild. Before I was burning through about half a quart of oil for every tank of gas.

My only regret is not having enough Federal Reserve Notes to put cams in it too.